The production of multiaxial warp knit fabrics by the incorporation of reinforcing threads as weft, warp and diagonal threads is already known. DE-A 33 04 345 describes, for example, a warp knit cloth with a normal warp knit fabric as the cloth ground and with reinforcing threads inserted into the latter. Weft threads run parallel to one another and are arranged in each case between two stitch heads of successive stitch rows and, in addition, two sets of diagonal threads are provided, which in each case run alternately between two stitch heads of stitch rows succeeding one another in the knitting direction. In this version, there are in the warp, weft and diagonal directions reinforcing threads which are not pricked through by the knitting needles. All the reinforcing threads are arranged at an angle of 45xc2x0 to one another, which, however, as a consequence of the method cannot be modified.
1. Technical Field
The invention relates to a method for the production of multiaxial warp knit fabrics with extended threads in the longitudinal, transverse and diagonal directions as a result of the direct insertion of the diagonal threads as weft sections onto the backs of the rising needles. The textile structures produced by the method are used, by virtue of their high stability and strength in the various directions, as reinforcement in composite materials, for example in automobile construction, rail vehicle construction and the aeronautic industry.
2. Prior Art
The production of multiaxial warp knit fabrics by the incorporation of reinforcing threads as weft, warp and diagonal threads is already known. DE-A 33 04 345 describes, for example, a warp knit cloth with a normal warp knit fabric as the cloth ground and with reinforcing threads inserted into the latter, in which weft threads run parallel to one another and are arranged in each case between two stitch heads of successive stitch rows and, in addition, two sets of diagonal threads are provided, which in each case run alternately between two stitch heads of stitch rows succeeding one another in the knitting direction. In this version, there are in the warp, weft and diagonal directions reinforcing threads which are not pricked through by the knitting needles. All the reinforcing threads are arranged at an angle of 45xc2x0 to one another, which, however, as a consequence of the method cannot be modified.
A special warp knitting machine for the processing of multiaxial contextures is also known, in which up to seven thread plies are suspended in a transport chain (90xc2x0/xc2x1 diagonal/90xc2x0/xe2x88x92diagonal/90xc2x0/+diagonal/90xc2x0) and are consolidated in the region of the knitting point by means of a warp knit weave. A 0xc2x0 thread system may be laid in place as the last thread ply directly in front of the knitting point. However, the knitting operation makes it necessary to prick through the closely layered thread plies, thus leading to the displacement of the threads. The consequences of this are a reduction in the cloth strength and an uneven defective structure density (Melliand Textile Reports 11/86, pages 804 to 806).
By means of the stitch-bonding machine, Malimo type, with multiaxial weft insertion, it is possible to produce multiaxial knit fabrics, for example with a thread ply combination of 0xc2x0/xe2x88x9290xc2x0/xe2x88x9245xc2x0/xe2x88x9290xc2x0/xc2x145xc2x0 in the case of angular deviations of 1 to 5xc2x0, that is to say the weft threads are not exactly parallel (Kettenwirk-praxis [Warp Knitting Practice] 2/94, pages 15 to 17).
In the multiaxial knitting technique for the production of industrial textiles on a right/left flat knitting machine, the multiaxial thread insertion is carried out by means of a combination of threads in the directions 0xc2x0/90xc2x0/xc2x145xc2x0 (ITB Vliesstoffexe2x80x94technische Textilien [ITB nonwoven textiles] 1/95, pages 44 to 45). The particular feature of this knitted fabric is that the threads running diagonally and vertically (0xc2x0) alternate after every second row on the front side and rear side of the cloth. The thread run for the warp threads and diagonal threads from the front side to the rear side of the sheetlike structure is implemented by additional drives for the feed elements, one for controlling the crossing movement and one for controlling the racking movement, which is executed it a revolving manner. This tying-in technique is intended primarily to prevent the delamination which occurs it the case of composite materials.
A biaxial knitting technique and a biaxially reinforces multiply knitted fabric are known from DE 49 19 985 A1. Altogether five weft systems can be inserted at right angles with crossing (90xc2x0/0xc2x0/90xc2x0/0xc2x0/90xc2x0) on a right/right flat knitting machine. Due to the arrangement of the thread plies (0xc2x0/xc2x090xc2x0), it is not possible to produce multiaxial knitted fabrics. Moreover, the 0xc2x0 thread plies are pricked through by the emerging needles, thus leading to the same disadvantages as in the special warp knitting machine.
Furthermore, several patent specifications (DD 268 720, DD 268 721, DD 258 722, DD 268 723, DD 268 729, DD 256 885) disclose variants for the production of multiaxial devices, in particular for stitch-bonding machines, by means of which an improvement in the quality of multiaxial sheetlike structures at a reduced mechanical outlay and a variable configuration due to the feed of finite thread sections from thread storage cartridges are to be achieved.
In the techniques which work on the basis of presented thread groups, as a consequence of the principle the 0xc2x0 thread plies always form the covering layer, with the result that the isotropy of the composite structure is impaired in the case of the multiply structures to be achieved. Some of the known multiaxial structures possess thread systems crossing at right angles, which cannot satisfy the requirements as to fiber angles (no greater than 45xc2x0) the known devices for the insertion of thread groups into transport chains make it possible to vary the guide angle of the diagonal threads within certain limits, but not when the machine is running.
The object of the present invention is to provide a method for the production of knitted reinforcing structures with a multiple variable multiaxial thread run, by means of which the thread angle can be changed as a function of the required force line runs, with the machine running, in the region of the diagonal and 90xc2x0 threads. At the same time, the pricking through of thread plies or the pricking on of threads is to be avoided, in order to ensure cost-effective production.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a method for the production of multiaxial warp knit fabrics with extended threads in the longitudinal, transverse and diagonal directions as a result of the direct insertion of the diagonal threads as weft sections onto the backs of the rising needles of the needle bars. At least two diagonal thread systems are simultaneously inserted contrarily as part wefts for each needle bar on a right/right warp knitting machine.
In another embodiment, 0xc2x0 threads are inserted as upright wefts between the diagonal thread systems.
In yet another embodiment of the invention 90xc2x0 threads are simultaneously inserted as through wefts in line with the stitch rows. The 90xc2x0 threads, in still a further embodiment, are partially discontinued or continue to operate as a part weft.
In an additional embodiment of the invention 0xc2x0 threads are additionally run in, and are racked laterally at a distance from one another.
In still another embodiment, the diagonal threads are discontinued according to the pattern and run as 0xc2x0 threads.
The advantages achieved by nears of the invention are, in particular, that, by means of the right/right warp knitting machine, weft insertion in line with the stitch rows can take place, while, due to the simultaneous contrary insertion of the diagonal threads on the front and rear needle bar, four diagonal thread systems for each complete stitch row can be tied in at a low outlay. Another advantage is that the 0xc2x0 threads are fed and tied in directly between the contrarily moved weft threads. The pricking through of the threads is ruled out in this procedure, so that a better utilization of substance is possible, as compared with multiaxially knitted contextures. By virtue of the direct weft insertion, there is no need for a prior production of the contexture (suspension of the thread groups inserted at an angle in the transport chains), so that there is a direct control of the racking distance of the weft threads in the region of the knitting zone. It is thereby possible to change the guide angle of the diagonal threads according to the force lines. 90xc2x0 threads may likewise be brought, as desired, into a 0xc2x0 position, with the result that differentiated layer thicknesses can be produced in a varying sequence.
Moreover, by means of the tying elements of a coarse three-dimensional right/right warp knit structure, the multiaxially layered threads are substantially reinforced in the z-direction and consequently the resistance to delamination is improved considerably.